Brush motor

ABSTRACT

A brush motor includes: a rotor core provided in a rotor; s teeth provided in the rotor core; s concentrated-winding coils with electric wires being respectively wound around the teeth; a commutator provided on the rotor in a relatively non-rotatable manner; c commutator pieces provided in the commutator and connected to the coils; p pairs of magnet magnetic poles provided on a stator and arranged to face the teeth; and a brush that is brought into sliding contact with the commutator pieces to supply a current to the coils, in which 0.5&lt;p/s&lt;1 and s&lt;c.

BACKGROUND Technical Field

The present disclosure relates to a brush motor in which a coil isenergized from a brush through a commutator.

Related Art

Conventionally, a brushed DC motor in which the number of coils islarger than the number of field magnetic poles has been known. Anexample of such a motor is a four-pole/six-slot motor having aconcentrated-winding structure (structure in which an electric wire ofcoils is individually wound around teeth, respectively) having fourfield magnetic poles and six iron core grooves (slots). In this motor,coils as many as the number of iron core grooves are provided, and sixcoils more than four, which is the number of field magnetic poles, areincorporated (see JPH11-69747).

SUMMARY

In the motor including the coils having the concentrated-windingstructure, in a case where the number of coils is larger than the numberof field magnetic poles, a blade angle in a cross section perpendicularto a rotation axis of the motor becomes smaller than a magnet angle. Asa result, a magnet magnetic flux is insufficiently picked up, and thereis a problem that it is difficult to effectively utilize the magneticflux. In addition, in a case where a coil having a straddling windingstructure in which an electric wire is wound so as to straddle aplurality of teeth is adopted, there is a problem that it is difficultto increase torque because a coil end bulges so that winding resistanceincreases.

One object of the present disclosure is to provide a brush motor thathas been created in light of the above problems and is capable ofachieving downsizing and high torque with a simple configuration. Notethat the present disclosure is not limited to this object, and it isalso possible to position, as another object of the present disclosure,achieving functions and effects that are derived from each configurationillustrated in “DETAILED DESCRIPTION” to be described later, thefunctions and effects being hardly obtained by conventional techniques.

A brush motor according to an embodiment of the present disclosureincludes: a rotor core provided in a rotor; s teeth provided in therotor core; s concentrated-winding coils with electric wires beingrespectively wound around the teeth; a commutator provided on the rotorin a relatively non-rotatable manner; c commutator pieces provided inthe commutator and connected to the coils; p pairs of magnet magneticpoles provided on a stator and arranged to face the teeth; and a brushthat is brought into sliding contact with the commutator pieces tosupply a current to the coils, in which the following inequality A andinequality B hold.

0.5<p/s<1  (Inequality A)

s<c  (Inequality B)

According to the disclosed technology, the magnet magnetic flux can besufficiently picked up, and the downsizing and the high torque can beachieved with a simple configuration.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded perspective view of a brush motor as a firstexample;

FIG. 2 is a perspective view of a rotor incorporated in the brush motorof FIG. 1;

FIG. 3 is a cross-sectional view of the brush motor of FIG. 1;

FIG. 4 is a view illustrating a magnet angle and a blade angle of thebrush motor of FIG. 1;

FIG. 5 is a circuit diagram illustrating a structure of a power supplycircuit in the brush motor of FIG. 1;

FIG. 6A is a view illustrating a brush motor (with four poles and sixslots) as a comparative example, and FIG. 6B is a view illustrating thebrush motor (with four poles and three slots) of FIG. 1;

FIG. 7A is a view illustrating a brush motor (having no commutatingpole) as a comparative example, and FIG. 7B is a view illustrating thebrush motor (having a commutating pole) in FIG. 1;

FIG. 8 is a cross-sectional view of a brush motor as a second example;

FIG. 9 is a view illustrating a magnet angle and a blade angle of thebrush motor of FIG. 8;

FIG. 10 is a circuit diagram illustrating a structure of a power supplycircuit in the brush motor of FIG. 8;

FIG. 11 is a cross-sectional view of a brush motor as a third example;

FIG. 12 is a view illustrating a magnet angle and a blade angle of thebrush motor of FIG. 11;

FIG. 13 is a circuit diagram illustrating a structure of a power supplycircuit in the brush motor of FIG. 11; and

FIG. 14 is a graph for describing a magnet angle of a ring magnet.

DETAILED DESCRIPTION 1. First Example [A. Configuration]

FIG. 1 is an exploded perspective view illustrating main components of abrush motor 1 (brushed motor) as a first example. The brush motor 1includes a stator 3 (stator), a rotor 6 (rotor), and a shaft 20. Thestator 3 and the rotor 6 are accommodated in a housing 2 formed in abottomed cylindrical shape as illustrated in FIG. 1. In FIG. 1, thedescription of a lid member (end bell) that closes an open end (left endin FIG. 1) of the housing 2 is omitted. The shaft 20 is a shaft-shapedmember supported by the housing 2 and the end bell via a bearing (notillustrated). The stator 3 is fixed to the housing 2, and the rotor 6 isfixed to the shaft 20 and rotates integrally with the shaft 20. Acentral axis of the shaft 20 coincides with a rotation axis C of therotor 6.

The stator 3 is provided with a magnet 4 (permanent magnet) for forminga magnetic field to be applied to the rotor 6. The magnet 4 has p pairsof magnet magnetic poles 5 formed in a curved surface shape. A shape ofthe magnet magnetic pole 5 is, for example, an arc surface shape or ashape similar thereto. The magnet magnetic poles 5 are attached along aninner peripheral surface of the housing 2 and arranged at predeterminedintervals in the circumferential direction (circumferential direction ofa circle centered on the rotation axis C in a cross sectionperpendicular to the rotation axis C). An orientation of a magneticfield is set to a direction from the outside to the inside of thehousing 2 or the opposite direction (direction from the inside to theoutside). In the present disclosure, the magnet magnetic poles 5 arearranged such that orientations of the magnetic fields are reversedbetween the adjacent magnet magnetic poles 5.

The magnet 4 illustrated in FIG. 1 is formed by combining four magnetpieces in which one magnetic pole pair is magnetized in one piece, butmay be formed by combining magnet pieces in which a plurality ofmagnetic pole pairs is magnetized in one piece. Alternatively, a tubularmagnet (ring magnet) that is not divided into a plurality of magnetpieces may be used as the magnet 4. In the ring magnet, the plurality ofmagnet magnetic poles 5 (magnetized regions) is adjacently arranged inthe circumferential direction, but a non-magnetized region may beprovided between the magnet magnetic poles 5. The non-magnetized regionis a region that does not substantially contribute to formation of themagnetic field with respect to the rotor 6, and is a portioncorresponding to a gap between the magnet magnetic poles 5 illustratedin FIG. 1. In this manner, it is unnecessary for a physical divisionnumber of the magnet 4 to match a magnetic division number.

The rotor 6 is provided with a core 10 (rotor core) and a commutator 8(commutator) that are fixed to the shaft 20 in a relativelynon-rotatable manner. The core 10 is formed by laminating a plurality ofsteel plates having the identical shape. A lamination direction of thesteel plates is identical to an extending direction of the rotation axisC. The core 10 is provided with s teeth 11 having a shape radiallyprotruding from the rotation axis C in the cross section perpendicularto the rotation axis C. Electric wires are wound respectively around theteeth 11 to form s coils 7 (concentrated-winding coils).

The commutator 8 is a member for energizing the coil 7 at an appropriateposition according to a rotation angle of the rotor 6 in an appropriateorientation. The commutator 8 is provided with c commutator pieces 9formed in a curved surface shape. A shape of the commutator piece 9 isformed in, for example, an arc surface shape or a shape similar thereto.These commutator pieces 9 are adjacently arranged in the circumferentialdirection along an outer peripheral surface of the shaft 20. Each of thecommutator pieces 9 and each of the coils 7 are connected by a powersupply circuit 23. A circuit structure of the power supply circuit 23will be described later.

A brush 21 (brush) is provided in the periphery of the commutator 8 soas to be in contact with the surface of the commutator piece 9. Thebrush 21 is attached to one end of a brush arm 22 and is supported in astate of being elastically pressed against the commutator piece 9. Inaddition, a pair of the brushes 21 and a pair of the brush arms 22 areprovided. The other ends of the brush arms 22 pass through, for example,the lid member, extend to the outside of the housing 2 and serve asterminals for power supply.

The brushes 21 are provided so as to be in contact with any one of the ccommutator pieces 9.

Regarding the relationship among the p pairs of magnet magnetic poles 5,the s coils 7, and the c commutator pieces 9, values of p, s, and c areset such that the following inequalities hold in the present disclosure.That is, a value obtained by dividing the number p of sets (the numberof pairs including two as one set) of the magnet magnetic poles 5 by thenumber s of the coils 7 is set to be larger than 0.5 and smaller than 1.In addition, the number s of the coils 7 is set to be smaller than thenumber c of the commutator pieces 9.

0.5<p/s<1  (Inequality A)

s<c  (Inequality B)

Note that, “p<s<2p” is obtained if Inequality A is transformed.Therefore, it suffices that the number s of the coils 7 is set to belarger than the number p of sets of the magnet magnetic poles 5 andsmaller than the total number 2p of the magnet magnetic poles 5.

FIG. 2 is a perspective view illustrating the rotor 6 including the core10 from which the electric wire of the coil 7 is removed. Each of theteeth 11 has a column 12 and a blade 13. The column 12 is a portionextending radially outward of the rotor 6. In addition, the blade 13 isa portion having a curved surface shape (an arc surface shape or a shapesimilar thereto), expanded in the circumferential direction of the rotor6 from an outer end of the column 12, and is arranged so as to face themagnet magnetic pole 5 in a non-contact manner. The electric wire of thecoil 7 is wound around the column 12 in multiple times by aconcentrated-winding method.

FIG. 3 is a cross-sectional view of the stator 3 and the rotor 6. Here,a cross-sectional view of the commutator piece 9 is also displayed in asuperimposed manner for the sake of convenience. The brush motor 1includes two pairs of magnet magnetic poles 5, three coils 7, and sixcommutator pieces 9. A combination of (p, s, c) is (2, 3, 6), which is afour-pole/three-slot motor.

The core 10 of the brush motor 1 according to the first example includesa commutating pole 14. The commutating pole 14 is a portion radiallyextending from the rotation axis C of the rotor 6 to reinforce a flow ofa magnetic flux, and is provided integrally with the core 10. Asillustrated in FIG. 3, the commutating pole 14 is arranged between theadjacent teeth 11 in the cross section perpendicular to the rotationaxis C so as to partition between the coils 7. The commutating pole 14does not have the coil 7, and the electric wire of the coil 7 is notwound around the commutating pole 14. Note that a commutating pole blade16 may be formed at a distal end of the commutating pole 14 asillustrated in a second example to be described later. In addition, aslit 17 having a predetermined width is provided between the blade 13 ofthe tooth 11 and the commutating pole 14. As a result, a slit width W ina winding direction of the coil 7 (an extending direction of the column12 and a radial direction of the rotor 6) is secured.

FIG. 4 is a view illustrating a magnet angle θ_(M) and a blade angleθ_(W) of the brush motor 1. In the cross section perpendicular to therotation axis C, a range where the magnetized region of one magnetmagnetic pole 5 substantially covers the rotor 6 is expressed by anangle with respect to the rotation axis C, and this is referred to asthe magnet angle θ_(M). For example, in a case where the magnet 4 isdivided into a plurality of magnet magnetic poles 5 (a plurality ofmagnet pieces) as illustrated in FIG. 4, a central angle of a fan shapesurrounded by the magnet magnetic pole 5 and line segments connectingboth ends of the magnet magnetic pole 5 to the rotation axis C in thecross section perpendicular to the rotation axis C is defined as themagnet angle θ_(M). In addition, in a case where the magnet 4 is a ringmagnet, a range in which a magnetic force appears in the radialdirection without including a non-magnetized region is expressed by anangle with respect to the rotation axis C, and this range is defined asthe magnet angle θ_(M).

Note that both ends of the magnetized region when a plurality ofmagnetic poles is magnetized in the ring magnet or the single magnetpiece have an angle at which the magnetic flux density decreases from acenter position (magnetization center position) of each magnetic pole,and the magnetic flux density first becomes zero. The relationshipbetween a magnetic flux density distribution of the ring magnet and themagnet angle θ_(M) is illustrated in FIG. 14. Angles θ₀ to θ₁₂ in FIG.14 represent angles at which the magnetic flux density becomes zero. Asillustrated in FIG. 14, a non-magnetized region or a minute polarityinversion region may be generated in the vicinity of 0° (θ₀ to θ₁), 90°(θ₂ to θ₄), 180° (θ₅ to θ₇), and 270° (θ₈ to θ₁₀), which correspond to aswitching point with an adjacent magnetic pole, and the magnet angleθ_(M) is defined excluding such ranges. In FIG. 14, as indicated by θ₁to θ₂, θ₄ to θ₅, θ₇ to θ₈, and θ₁₀ to θ₁₁, an angular range from when anabsolute value of the magnetic flux density exceeds zero to when themagnetic flux density includes the center position of each magnetic poleand reaches 0 again is defined as the magnet angle θ_(M). In any case,the angle formed by the magnetized region of one magnet magnetic pole 5and the rotation axis C in the cross section perpendicular to therotation axis C is defined as the magnet angle θM.

In addition, a range in which one blade 13 faces the magnet 4 in thecross section perpendicular to the rotation axis C is expressed by anangle with respect to the rotation axis C, and this is referred to as ablade angle θ_(W). That is, a central angle of a fan shape surrounded bythe blade 13 and line segments connecting both ends of the blade 13 tothe rotation axis C in the cross section perpendicular to rotation axisC is defined as the blade angle θ_(W). In the brush motor 1 of the firstexample, the blade angle θ_(W) is preferably set to the magnitude of themagnet angle θ_(M) or more (θ_(W)≥θ_(M)). As a result, the magnetmagnetic flux is easily picked up by the teeth 11, and the magnetic fluxis effectively utilized.

FIG. 5 is a circuit diagram illustrating a structure of the power supplycircuit 23. The s coils 7 are annularly connected. In FIG. 5, threecoils 7 are connected by a delta connection method (triangle connectionmethod). In addition, the c (six in FIG. 5) commutator pieces 9 areshort-circuit connected to an annular coil circuit every 360/p degrees(every 180 degrees in FIG. 5) with respect to the rotation angle of therotor 6. Note that C₁ to C₆ in FIG. 5 represent six commutator pieces 9.For example, on the annular coil circuit illustrated in FIG. 5, a pointP₁ between the first coil and the second coil is short-circuit connectedto the commutator pieces C₁ and C₄. Positions of these commutator piecesC₁ and C₄ are shifted by 180 degrees with respect to the rotation axisC. Therefore, a potential at the point P₁ becomes identical every timethe rotation axis C makes a half turn. Similarly, a point P₂ between thesecond coil and the third coil is short-circuit connected to thecommutator pieces C₂ and C₅, and a point P₃ between the third coil andthe first coil is short-circuit connected to the commutator pieces C₃and C₆.

In FIG. 5, B₁ and B₂ represent two brushes 21. Positions of the brushesB₁ and B₂ are shifted by 90 degrees with respect to the rotation axis C.One brush 21 is connected to a positive pole of a power supply, and theother brush 21 is connected to a negative pole of the power supply. Eachof the brushes B₁ and B₂ is connected to one of the commutator pieces C₁to C₆. Among the six commutator pieces 9, the commutator piece 9connected to the brush 21 varies according to the rotation angle. Forexample, a combination of the commutator pieces 9 connected to thebrushes B₁ and B₂ varies as (C₆C₁, C₂), (C₁, C₂), (C₁C₂, C₃), (C₂, C₃)and so on as the rotor 6 rotates. With such a circuit configuration, therotor 6 is appropriately rotationally driven with high torque.

[B. Functions and Effects]

FIG. 6A is a view illustrating a brush motor (with four poles and sixslots) as a comparative example. In this brush motor, the number ofcoils 7 is 6, which is more than that in the first example, the numberof pairs p of magnet magnetic poles 5 is two pairs, which is identicalto that in the first example, and a magnet angle θ_(M) is slightlysmaller than 90 degrees. On the other hand, a blade angle θ_(W) is only60 degrees at the maximum since the number of coils is 6, and the bladeangle θ_(W) becomes smaller than the magnet angle θ_(M). As a result, amagnet magnetic flux is insufficiently picked up, and it is difficult toeffectively utilize the magnetic flux.

On the other hand, in the brush motor 1 (with four poles and threeslots) of the first example, the number of coils is three, and thus, theblade angle θ_(W) increases as illustrated in FIG. 6B. As a result, thearea of the blade 13 facing the magnet magnetic pole 5 is secured, andthus, the magnet magnetic flux is easily picked up by the teeth 11, andthe magnetic flux is effectively utilized.

FIG. 7A is a view illustrating a brush motor (having no commutatingpole) as a comparative example. When a core 10 does not include acommutating pole 14, a flow of a magnetic flux applied from a magnetmagnetic pole 5 to a core 10 becomes intermittent, and vibration(cogging) is likely to increase. For example, a magnetic flux indicatedby a white arrow in FIG. 7A is not applied to the core 10 in a statewhere a relatively wide portion of the slit 17 faces the magnet magneticpole 5. In addition, there is a possibility that an eddy current isgenerated in a housing 2 to increase a loss. Further, a permeancecoefficient decreases, and there is a possibility that demagnetizationeasily occur.

On the other hand, the brush motor 1 of the first example includes thecommutating pole 14 and the slit 17 that is relatively narrow, and thus,the flow of the magnetic flux becomes continuous. For example, asindicated by a black arrow in FIG. 7B, the magnetic flux is applied tothe core 10 even in a state where the commutating pole 14 and theportion of slit 17 face the magnet magnetic pole 5. As a result,vibration (cogging) is likely to decrease. In addition, an eddy currentis hardly generated in the housing 2, and a loss is reduced. Inaddition, a permeance coefficient increases to make demagnetizationdifficult, and winding rotor balance is also improved.

According to the brush motor 1 of the first example, the followingeffects can be obtained.

(1) In the brush motor 1 of the first example, the values of p, s, and care set such that 0.5<p/s<1 and s<c hold. As a result, the size of thebrush motor 1 can be easily reduced, or the higher torque can beachieved with the same size (the same volume), for example, as comparedwith an existing brush motor as illustrated in FIG. 6A. In addition, themagnetic flux can be effectively utilized since the blades 13 of theteeth 11 easily face the magnet magnetic poles 5 with a sufficientlylarge area. Therefore, the magnet magnetic flux can be sufficientlypicked up, and the downsizing and the high torque can be achieved with asimple configuration.

In addition, since a width direction of the slit 17 approaches parallelto a winding direction of the winding as compared with the existingbrush motor, the net slit width W can be increased, and the winding canbe easily wound. In addition, the number of winding steps decreases, andlabor and cost required for manufacturing can be reduced.

(2) In the brush motor 1 of the first example, the blade angle θ_(W) isset to be equal to or larger than the magnet angle θ_(M) as illustratedin FIG. 6B. As a result, the area of the blade 13 facing the magnetmagnetic pole 5 can be secured, and the magnetic flux can be effectivelyutilized reliably. In addition, the vibration (cogging) can be reducedas compared with the case where the blade angle θ_(W) is smaller thanthe magnet angle θ_(M). Further, the slit width W can be increased byincreasing the blade angle θ_(W), and the winding can be easily wound.

(3) As illustrated in FIG. 7B, the brush motor 1 of the first exampleincludes the commutating pole 14. Since such a commutating pole 14 isprovided, the flow of the magnetic flux exchanged between the magnetmagnetic pole 5 and the core 10 can be made continuous, and thevibration (cogging) can be reduced. In addition, the generation of theeddy currents in the housing 2 can be prevented, and the loss can bereduced. In addition, demagnetization can be made difficult byincreasing the permeance coefficient, and the winding rotor balance canbe improved.

(4) In the brush motor 1 of the first example, the coils 7 are connectedin an annular shape as illustrated in FIG. 5. Further, with respect tothe annular coil circuit, each of the commutator pieces 9 isshort-circuit connected every 180 degrees (every 360/p degrees) withrespect to the rotation angle of the rotor 6. With such a circuitconfiguration, the number of brushes can be reduced to 1/p as comparedwith the existing brush motor, the size of the brush motor 1 can beeasily reduced, and the downsizing and the high torque can be achievedwith a simple configuration.

(5) The brush motor 1 of the first example includes the two pairs ofmagnet magnetic poles 5, the three coils 7, and the six commutatorpieces 9, and thus, the combination of (p, s, c) is (2, 3, 6). With sucha configuration, the brush motor 1 having the high torque can beachieved with a simple configuration in which the number of coils issmall, and the downsizing is easy due to an increase in magnetic flux.

2. Second Example

FIG. 8 is a cross-sectional view illustrating a structure of a brushmotor 41 as a second example. Here, a cross-sectional view of a stator 3and a rotor 6 is displayed to be superimposed on a cross-sectional viewof a commutator piece 9 for the sake of convenience. Elementscorresponding to the elements described in the first example are denotedby the identical reference signs, and the description thereof isappropriately omitted. The brush motor 41 includes three pairs of magnetmagnetic poles 5, four coils 7, and twelve commutator pieces 9. Acombination of (p, s, c) is (3, 4, 12), which is a six-pole/four-slitmotor.

A commutating pole 14 provided on a core 10 of the brush motor 41according to the second example includes a commutating pole column 15and a commutating pole blade 16. As illustrated in FIG. 8, thecommutating pole column 15 is a portion extending radially outward ofthe rotor 6. In addition, the commutating pole blade 16 is a portionhaving a curved surface shape (an arc surface shape or a shape similarthereto), expanded in the circumferential direction of the rotor 6 froman outer end of the commutating pole column 15, and is arranged so as toface the magnet magnetic pole 5 in a non-contact manner. Note that thecommutating pole 14 does not have the coil 7, and an electric wire ofthe coil 7 is not wound around the commutating pole 14. In addition, thecommutating pole blade 16 can be omitted, and the commutating pole 14having the same shape as that of the first example may be formed.

FIG. 9 is a view illustrating a magnet angle θ_(M) and a blade angleθ_(W) of the brush motor 41. In the brush motor 41 of the second exampleas well, the blade angle θ_(W) is preferably set to the magnitude of themagnet angle θ_(M) or more (θ_(W)≥θ_(M)). As a result, the magnetmagnetic flux is easily picked up by the teeth 11, and the magnetic fluxis effectively utilized.

Each of the commutator pieces 9 and each of the coils 7 are connected bya power supply circuit 42. FIG. 10 is a circuit diagram illustrating astructure of the power supply circuit 42. The four coils 7 are annularlyconnected. In addition, the twelve commutator pieces 9 are short-circuitconnected to the annular coil circuit every 360/p degrees (that is,every 120 degrees) with respect to the rotation angle of the rotor 6.For example, on the annular coil circuit illustrated in FIG. 10, a pointQ₁ between the first coil and the second coil is short-circuit connectedto commutator pieces C₁, C₅, and C₉.

Positions of these commutator pieces C₁, C₅, and C₉ are shifted by 120degrees with respect to a rotation axis C. Therefore, a potential of thepoint Q₁ becomes identical every time the rotation axis C rotates by ⅓.Similarly, a point Q₂ between the second coil and the third coil isshort-circuit connected to commutators pieces C₂, C₆, and C₁₀. Inaddition, a point Q₃ between the third coil and the fourth coil isshort-circuit connected to commutator pieces C₃, C₇, and C₁₁, and apoint Q₄ between the fourth coil and the first coil is short-circuitconnected to commutator pieces C₄, C₅, and C₁₂. In addition, positionsof brushes B₁ and B₂ are shifted by 180 degrees with respect to therotation axis C.

According to the brush motor 41 of the second example, similar effectsas those of the first example can be obtained. For example, downsizingcan be performed more easily or higher torque can be achieved with thesame size as compared with an existing brush motor. In addition, highertorque can be obtained as compared with the brush motor 1 of the firstexample. Meanwhile, the number of winding steps decreases with aconcentrated-winding structure, and labor and cost required formanufacturing can be reduced as compared with an existing brush motor(for example, a brush motor with six poles and twelve slots) in whichthe number of magnet magnetic poles 5 is identical to that of the brushmotor 41 of the second example and the number of coils is larger.Further, a coil end can be reduced with the concentrated-windingstructure, and winding resistance can be reduced. In addition, thepulsation of a current can be increased as compared with the firstexample, and the use of the pulsation of the current enables sensorlesscontrol that does not require an additionally required sensor magnet.

3. Third Example

FIG. 11 is a cross-sectional view illustrating a structure of a brushmotor 51 as a third example. Here, a cross-sectional view of a stator 3and a rotor 6 is displayed to be superimposed on a cross-sectional viewof a commutator piece 9 for the sake of convenience. Elementscorresponding to the elements described in the first example are denotedby the identical reference signs, and the description thereof isappropriately omitted. The brush motor 51 includes three pairs of magnetmagnetic poles 5, five coils 7, and fifteen commutator pieces 9. Acombination of (p, s, c) is (3, 5, 15), which is a six-pole/five-slitmotor. Note that a commutating pole 14 is omitted in a core 10 of thebrush motor 51 according to the third example. As a result, a slit widthW between adjacent blades 13 is secured, and an electric wire of thecoil 7 is easily wound.

FIG. 12 is a view illustrating a magnet angle θ_(M) and a blade angleθ_(W) of the brush motor 51. In the brush motor 51 of the third exampleas well, the blade angle θ_(W) is preferably set to the magnitude of themagnet angle θ_(M) or more (θ_(W)≥θ_(M)). As a result, the magnetmagnetic flux is easily picked up by the teeth 11, and the magnetic fluxis effectively utilized.

Each of the commutator pieces 9 and each of the coils 7 are connected bya power supply circuit 52. FIG. 13 is a circuit diagram illustrating astructure of the power supply circuit 52. The five coils 7 are annularlyconnected. In addition, the fifteen commutator pieces 9 areshort-circuit connected to the annular coil circuit every 360/p degrees(that is, every 120 degrees) with respect to the rotation angle of therotor 6. For example, on the annular coil circuit illustrated in FIG.13, a point R₁ between the first coil and the second coil isshort-circuit connected to commutator pieces C₁, C₆, and C₁₁.

Positions of these commutator pieces C₁, C₆, and C₁₁ are shifted by 120degrees with respect to a rotation axis C. Therefore, a potential of thepoint R₁ becomes identical every time the rotation axis C rotates by ⅓.Similarly, a point R₂ between the second coil and the third coil isshort-circuit connected to commutator pieces C₂, C₇, and C₁₂. Further, apoint R₃ between the third coil and the fourth coil is short-circuitconnected to commutator pieces C₃, C₅, and C₁₃, a point R₄ between thefourth coil and the fifth coil is short-circuit connected to commutatorpieces C₄, C₉, and C₁₄, and a point R₅ between the fifth coil and thefirst coil is short-circuit connected to commutator pieces C₅, C₁₀, andC₁₅. In addition, positions of brushes B₁ and B₂ are shifted by 180degrees with respect to the rotation axis C.

According to the brush motor 51 of the third example, similar effects asthose of the first example and the second example can be obtained. Forexample, downsizing can be performed more easily or higher torque can beachieved with the same size as compared with an existing brush motor. Inaddition, higher torque can be obtained as compared with the brushmotors 1 and 41 of the first example and the second example. Further, ascompared with the first example and the second example, the pulsation ofthe torque can be reduced, vibration can be reduced to enhance thecontrollability.

4. Others

The above examples are merely examples, and there is no intention toexclude applications of various modifications and technologies that arenot explicitly described in the present examples. The configurations ofthe present examples can be variously modified and implemented within ascope not departing from the gist thereof. In addition, theconfigurations of the present examples can be selected as necessary, orcan be appropriately combined with various configurations included inknown technologies.

[Description of Reference Signs] 1, 41, 51 brush motor 2 housing 3stator (stator) 4 magnet 5 magnet magnetic pole 6 rotor (rotor) 7 coil 8commutator 9 commutator piece 10 core (rotor core) 11 tooth 12 column 13blade 14 commutating pole 15 commutating pole column 16 commutating poleblade 17 slit 20 shaft 21 brush 22 brush arm 23, 42, 52 power supplycircuit θ_(W) blade angle θ_(M) magnet angle C rotation axis W slitwidth

What is claimed is:
 1. A brush motor comprising: a rotor core providedin a rotor; s teeth provided in the rotor core; s concentrated-windingcoils with electric wires being respectively wound around the teeth; acommutator provided on the rotor in a relatively non-rotatable manner; ccommutator pieces provided in the commutator and connected to the coils;p pairs of magnet magnetic poles provided on a stator and arranged toface the teeth; and a brush that is brought into sliding contact withthe commutator pieces to supply a current to the coils, whereinfollowing Inequality A and Inequality B hold:0.5<p/s<1  (Inequality A); ands<c  (Inequality B)
 2. The brush motor according to claim 1, wherein thetooth includes a blade formed in a curved surface shape expanding in arotation direction of the rotor along a surface of the magnet magneticpole, the magnet magnetic pole is formed in a curved surface shapefacing the blade, and a central angle of a fan shape, surrounded by theblade and line segments connecting both ends of the blade to therotation axis in a cross section perpendicular to the rotation axis ofthe rotor, is defined as a blade angle, an angle formed between amagnetized region of one of the magnet magnetic poles and the rotationaxis is defined as a magnet angle, and the blade angle is equal to orlarger than the magnet angle.
 3. The brush motor according to claim 1,further comprising at least one commutating pole that is providedintegrally with the rotor core between the adjacent coils, extendsradially from a rotation center of the rotor to reinforce a flow of amagnetic flux, and does not have a coil.
 4. The brush motor according toclaim 2, further comprising at least one commutating pole that isprovided integrally with the rotor core between the adjacent coils,extends radially from a rotation center of the rotor to reinforce a flowof a magnetic flux, and does not have a coil.
 5. The brush motoraccording to claim 1, further comprising a power supply circuit in whichthe s coils are annularly connected, and the c commutator pieces areshort-circuit connected every 360/p degrees with respect to a rotationangle of the rotor.
 6. The brush motor according to claim 4, furthercomprising a power supply circuit in which the s coils are annularlyconnected, and the c commutator pieces are short-circuit connected every360/p degrees with respect to a rotation angle of the rotor.
 7. Thebrush motor according to claim 1, wherein the p is two, the s is three,and the c is six.
 8. The brush motor according to claim 6, wherein the pis two, the s is three, and the c is six.
 9. The brush motor accordingto claim 1, wherein the p is three, the s is four, and the c is twelve.10. The brush motor according to claim 6, wherein the p is three, the sis four, and the c is twelve.
 11. The brush motor according to claim 1,wherein the p is three, the s is five, and the c is fifteen.
 12. Thebrush motor according to claim 6, wherein the p is three, the s is five,and the c is fifteen.